NOAA National Environmental Satellite, Data, and Information Service, Center for Satellite Applications and Research, E/RA3, College Park, MD, USA.
NOAA National Environmental Satellite, Data, and Information Service, Center for Satellite Applications and Research, E/RA3, College Park, MD, USA; CIRA at Colorado State University, Fort Collins, CO, USA.
Water Res. 2020 Jul 1;178:115839. doi: 10.1016/j.watres.2020.115839. Epub 2020 Apr 21.
It has been difficult in satellite remote sensing to derive accurate water optical, biological, and biogeochemical products over high-altitude inland waters due to issues in satellite data processing (i.e., atmospheric correction). In this study, we demonstrate that accurate normalized water-leaving radiance spectra nL(λ) can be derived for a high-altitude lake, Lake Tahoe, using improved Rayleigh radiance computations (Wang, M., Opt. Express, 24, 12414-12429, 2016) which accurately account for water surface altitude effects in the Multi-Sensor Level-1 to Level-2 (MSL12) ocean color data processing system. Satellite observations from the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (SNPP) between 2012 and 2018 are used to evaluate and validate satellite-derived nL(λ) spectra, and to quantitatively characterize water properties in the lake. Results show that VIIRS-derived nL(λ) spectra are quite comparable with those from the in situ measurements. Subsequent retrievals of water biological and biogeochemical products show that chlorophyll-a (Chl-a) concentration and Secchi depth (SD) are reasonably well-estimated, and captured normal seasonal variations in the lake, e.g., the annual highest Chl-a and SD normally occur in the winter while the lowest occur in the summer, which is consistent with in situ measurements. Interannual variability of these water quality parameters is also observed. In particular, Lake Tahoe experienced a significant environmental anomaly associated with an extreme weather condition event in 2017, showing considerably decreased nL(λ) at the spectral bands of 410, 443, and 486 nm, and significantly reduced SD values in the entire lake. The low SD measurements from VIIRS are consistent with in situ observations. Following the event in the 2017-2018 winter, Lake Tahoe recovered and returned to its typical conditions in spring 2018.
在卫星遥感中，由于卫星数据处理（即大气校正）方面的问题，难以准确地推导出高海拔内陆水体的水光学、生物和生物地球化学产品。在本研究中，我们证明了使用改进的瑞利辐射计算（Wang，M.，Opt. Express，24，12414-12429，2016）可以为高海拔湖泊太浩湖（Lake Tahoe）准确推导出归一化水出射辐射光谱 nL（λ），该计算方法准确地考虑了多传感器 1 级到 2 级（MSL12）海洋颜色数据处理系统中水面高度的影响。我们利用 2012 年至 2018 年期间搭载在 Suomi 国家极地轨道伙伴关系卫星（SNPP）上的可见红外成像辐射计套件（VIIRS）卫星观测数据来评估和验证卫星推导出的 nL（λ）光谱，并定量描述湖泊的水质特性。结果表明，VIIRS 推导出的 nL（λ）光谱与原位测量值非常吻合。随后对水生物和生物地球化学产品的反演表明，叶绿素 a（Chl-a）浓度和藻华透明度（SD）的估算值相当合理，并且能够捕捉到湖泊的正常季节性变化，例如，每年的最高 Chl-a 和 SD 通常出现在冬季，而最低值出现在夏季，这与原位测量值一致。还观察到这些水质参数的年际变化。特别是，2017 年，太浩湖经历了与极端天气条件事件相关的重大环境异常，在光谱波段 410、443 和 486nm 处的 nL（λ）明显降低，整个湖泊的 SD 值显著降低。VIIRS 测量的低 SD 值与原位观测结果一致。在 2017-2018 年冬季的事件之后，太浩湖在 2018 年春季恢复并恢复到典型状态。
